Condensation Risk Calculator

Analyse interstitial condensation risk using the Glaser method. Build a wall assembly, set boundary conditions, and check for moisture problems before they happen.

BS EN ISO 13788 · DIN 4108-3 · Glaser Method

Assembly Builder

(0 layers, 0 mm total)
INTERIOR (warm side)
EXTERIOR (cold side)
Add materials from the selector above to build your wall assembly.

Boundary Conditions

Interior (Warm Side)

°C
%

Exterior (Cold Side)

°C
%

Analysis Mode

Analyses a single worst-case design day. Quick check for condensation risk.

Configure inputs and calculate to see results

About Condensation Risk Calculator

The condensation risk calculator analyses interstitial condensation in wall, roof, and floor assemblies using the steady-state Glaser method per EN ISO 13788. It is used by building physicists and designers to find where water vapour may condense inside a construction before it causes damp, decay, or mould.

Build the assembly layer by layer, set the interior and exterior temperature and relative humidity, and the tool computes the temperature and vapour pressure profiles, flags any interface where the actual vapour pressure reaches saturation, and quantifies the resulting condensation rate.

How It Works

  1. Calculate the temperature at each interface by distributing the temperature drop in proportion to each layer thermal resistance.
  2. Compute the saturation vapour pressure at each interface from its temperature via the Magnus relation.
  3. Distribute the actual vapour pressure linearly with each layer vapour resistance between interior and exterior.
  4. Detect condensation where actual pressure exceeds saturation, clamp to saturation, and compute the condensation rate in g/m2 per month.

Worked Example

With interior 20 C / 50% RH and exterior -5 C / 90% RH, an interface that cools below its dew point shows actual vapour pressure above saturation, so the Glaser analysis flags a condensing interface and reports its accumulation rate.

Formulas

Interface temperature
T_i = Ti - (Ti - Te) * (R_cum / R_total)
Saturation vapour pressure
Ps = 610.5 * exp((17.269 * T) / (237.3 + T))
Vapour pressure profile
P_i = P_in - (P_in - P_out) * (G_cum / G_total)

Standards & References

  • EN ISO 13788
  • BS 5250
  • DIN 4108-3

Frequently Asked Questions

What is the Glaser method?

The Glaser method is a steady-state graphical procedure standardised in EN ISO 13788 that compares the saturation and actual vapour pressure profiles through an assembly to locate and quantify interstitial condensation.

What causes interstitial condensation?

It occurs when warm, moist interior air diffuses through the construction and reaches a layer cold enough that its saturation pressure falls below the local vapour pressure, so moisture condenses within the build-up rather than on the surface.

How can I reduce condensation risk in a wall?

Add a vapour control layer on the warm side, increase insulation on the cold side to keep inner layers warmer, or use a more vapour-open external layer so trapped moisture can dry outward. The tool suggests remedies automatically.

Is the condensation risk calculator free to use?

Yes, it runs entirely in your browser at no cost and stores none of your input data.